DE10348736A1 - Method and system for controlling a vehicle with a steering actuator - Google Patents

Abstract

The invention relates to a control system for a vehicle having a steering actuator and a plurality of sensors that generate a plurality of signals that correspond to a dynamic condition of the vehicle, and a plurality of sensors connected to a controller unit, the controller unit is suitable, depending on the measured vehicle conditions, to determine a coefficient of friction of the road surface, to determine a slip angle depending on the measured vehicle conditions, to determine a first change in the angle of the steering actuator in order to reduce the slip angle until the lateral force increases, determine a second change in the angle of the steering actuator in order to increase the slip angle until the lateral force decreases. A corresponding control method comprises the steps: determining a lateral force as a function of measured vehicle conditions; Determining a slip angle as a function of measured vehicle conditions; Determining a first change in the angle of the steering actuator in order to reduce the slip angle until the lateral force increases; Controlling the steering actuator in response to the first change in the angle of the steering actuator; thereafter, determining a second change in the angle of the steering actuator to increase the slip angle until the lateral force decreases; and controlling the steering actuator depending on the ...

Description

The invention relates to a system to control for a vehicle having a steering actuator for

Dynamic control systems for motor vehicles have been around for a short time various products offered. Dynamic control systems typically regulate the yaw behavior of the vehicle by controlling the braking force the different wheels of the vehicle. Yaw control systems typically compare the desired direction of the vehicle based on the angle of the steering wheel with the direction of travel. By regulating the strength of the Braking on either side of the vehicle can be the desired direction of travel to be kept.

When the vehicle is operating, a large side slip angle may occur on the front wheels in the event of severe understeer or oversteer. The lateral force typically generated by a tire reaches a maximum value F _latmax in the case of the tire slip angle which is designated as α _p . The maximum lateral force decreases or normalizes as the slip angle increases further. Normalizing is commonly referred to as the saturation range. A problem with using the braking force to control the yaw of the vehicle is that the yaw moment is controlled without considering the side forces. Direct control of the lateral force cannot be achieved using a braking system alone.

Therefore, the problem underlying the invention is to provide a method and a system that can control the yaw of the vehicle near the maximum lateral force F _{latmax in} order to obtain maximum control over the vehicle.

According to the invention, the problem is solved by the characteristics of the claims 1 and 7. Further developments of the invention are described in the dependent claims.

The present invention uses a steer-by-wire system that can change the relationship between the angle of the road _wheels and the angle of the steering wheel to operate the vehicle with almost maximum lateral force F _latmax .

In one aspect of the invention comprises a tax system for the stability of a motor vehicle a variety of sensors that the dynamic Determine the conditions of the vehicle. With the sensors is a controller unit connected. The controller unit determines a coefficient of friction for the surface of the Road, calculates the maximum slip angle based on the coefficient of friction the surface the street, determines a calculated side slip angle as a function of from the measured dynamic conditions for the vehicle and reduced the angle of a steering wheel actuator if the calculated side slip angle larger than is the maximum slip angle.

In a second aspect of the invention includes a tax system for the stability of a motor vehicle a variety of sensors that the dynamic Determine the conditions of the vehicle. With the sensors is a controller unit connected. The controller unit determines a lateral force as a function of it from the measured conditions for the vehicle determines a slip angle depending on the measured conditions for the vehicle determines a first change in the angle of the steering actuator, to reduce the slip angle until the lateral force elevated, after which a second change of the angle of the steering actuator is determined by the slip angle as long as increase until the lateral force decreases.

In a third aspect of the invention comprises a method for controlling a vehicle with a steering actuator determining a coefficient of friction for the surface of the Road, Calculate a maximum allowable Determine slip angle based on the coefficient of friction of the surface of the road a calculated side slip angle depending on the measured dynamic conditions for the vehicle and reducing the angle of a steering wheel actuator, if the calculated side slip angle is greater than the maximum permitted slip angle is.

In a fourth aspect of the invention comprises a method for controlling a vehicle with a steering actuator: the determination of a lateral force depending on the measured Conditions for the vehicle, determining a slip angle depending from the measured conditions for the Vehicle, determining a first change in the angle of a steering actuator, to reduce the slip angle until the lateral force increases taxes of the steering actuator depending from the first change the angle of the steering actuator, after that, determining a second change the angle of the steering actuator to increase the slip angle until the lateral force decreases and control of the steering actuator in dependence from the second change the angle of the steering actuator.

An advantage of the invention is in that such systems are simple in a steer-by-wire system can be used. On Another advantage is that the slip angle is the peak the lateral force corresponds to the load regardless of the tires and, in some cases, of the coefficient of friction of the surface.

These and other advantages and features of the present invention will hereinafter be described one embodiment explained or disclosed in connection with the drawing.

Show it:

1 a front view of a motor vehicle and various operating parameters of a Vehicle trying to perform a turning maneuver;

2A a plan view of a motor vehicle and various operating parameters of a vehicle trying to perform a turning maneuver;

2 B a plan view of a tire and the forces acting thereon;

3 a block diagram showing a portion of a microprocessor associated with sensors and controlled devices that may be present in a system in accordance with the present invention;

4 a representation of the lateral forces acting against the slip angle for three different values of the coefficient of friction;

5 a logic workflow block diagram according to a first embodiment of the present invention;

6 a logical workflow block diagram according to a second embodiment of the present invention.

The present invention is for use in yaw control systems provided with electronically controlled and / or electrically operated Steering systems of motor vehicles are equipped. The invention however can easily be for the use in other motor vehicle systems is adapted, such as active tilt controls, roll controls or active Suspension controls. The invention is explained using a front-steered vehicle, however, the teachings contained therein also on rear wheel steering systems or All-wheel steering systems are applied.

With reference to the 1 . 2A and 2 B illustrates various operating parameters and variables used by the present invention that relate to the application of the present invention to a ground-based motor vehicle 10 Respectively. One skilled in the art will instantly recognize the physical basics represented by these illustrations, making it easy to adapt to different types of vehicles. The lateral acceleration is denoted by a _y , the longitudinal acceleration is denoted by a _x , the yaw rate is denoted by r and the angle of the steering wheel to the vehicle longitudinal axis A is δ.

With reference to 3 has a stability control system 24 a controller unit 26 that is used to receive information from a variety of sensors that include a yaw rate sensor 28 , a speed sensor 30 , a lateral acceleration sensor 32 , a roll rate sensor 34 , a steering angle sensor 35 , a longitudinal acceleration sensor 36 , a pitch rate sensor 37 can include. A sensor 39 can also be provided for the steering angle position. The sensor 39 provides information regarding the controlled position of the road bike. The lateral acceleration, the longitudinal acceleration, the yaw rate, the roll course and the speed can be determined using a global positioning system (GPS). The controller unit regulates on the basis of the inputs from the sensors 26 the steering angle. Depending on the desired sensitivity of the system and various other factors, it may not be all of the sensors 28-37 can be used in a commercial embodiment. The sensors can also determine other factors, such as the coefficient of friction (or surface coefficient my, μ), the lateral forces on the tires F _lat and the side slip angle.

The roll rate sensor 34 and the pitch rate sensor 37 can determine the rolling conditions for a vehicle rollover system by sensing the height of one or more points of the vehicle relative to the surface of the road. The rollover system can use the knowledge available here to prevent the vehicle from rolling over. Sensors that can be used to do this include a lidar or radar-based distance sensor, a laser-based distance sensor, and a sonar-based distance sensor.

The roll rate sensor 34 and the pitch rate sensor 37 can also determine the rolling conditions by determining the relative linear or rotational displacement or the displacement speed of one or more components of the chassis, with a linear height or distance sensor, a rotation height or distance sensor, a wheel speed sensor, a steering wheel position sensor. Sensor, a steering wheel speed sensor and a heading input device of an electronic component for the driver, which can have a steer-by-wire control using a handwheel or a joystick.

The rolling conditions can also can be determined by the force or torque that corresponds to the loading conditions correspond to one or more parts of the suspension or chassis, are recorded, with a pressure transducer in the case of an active suspension, a shock absorber sensor, such as a load cell, a strain gauge, the absolute or relative engine load of the steering system, the pressure the hydraulic lines of the steering system, a tire lateral force sensor or sensors, a tire longitudinal force sensor, a tire vertical force sensor or a tire sidewall torsion sensor, can be present.

The speed sensor 30 can be one of the variety of speed sensors known to those skilled in the art. For example, a suitable speed sensor can have a sensor on each wheel sen, being from the controller unit 26 an average is determined. The controller unit preferably converts the wheel speed into the speed of the vehicle. The yaw rate, the steering angle, the wheel speed and possibly a slip angle, which are calculated on each wheel, can be converted into the speed of the vehicle at its center of gravity (V _CG ). Various other algorithms are known to those skilled in the art. The speed can also be obtained via a transmission sensor. For example, if the speed is determined while the vehicle is accelerating or braking at a corner, the lowest or the highest wheel speed are not used, as this leads to incorrect results.

The rolling behavior of the vehicle can also be determined by the following translational or rotational movement-dependent positions, speeds or accelerations of the vehicle, which are performed by a rollover gyro, the roll rate sensor 34 , the yaw rate sensor 28 , the lateral acceleration sensor 32 , a vertical acceleration sensor, a vehicle longitudinal acceleration sensor, a side or vertical speed sensor including a sensor based on the wheel speed, a radar-based speed sensor, a sonar-based speed sensor, a laser-based speed sensor or an optical one Speed sensor can be detected.

The steering control 38 can be the position of an actuator 40A the right front wheel, an actuator 40B the left front wheel, an actuator 40C of the left rear wheel and an actuator 40D the right rear wheel. As has already been described above, however, two or more of the actuators can be controlled simultaneously as one actuator. For example, in a conventional rack and pinion system, the two front wheels connected to it can be controlled simultaneously. A rear control can also be realized with a rack and pinion system. Based on the inputs from the sensors 28 to 39 determines the controller unit 26 a rolling condition and controls the steering position of the wheels.

The controller unit 26 can also control the brakes 42 use that with the front right brakes 44A , the front left brakes 44B , the rear left brakes 44C and the rear right brakes 44D connected is. When using the brakes in addition to steering control, some control advantages can be achieved. That means the controller unit 26 may be used to achieve braking force distribution on the brake actuators as described in US Pat. No. 6,263,261, which is incorporated herein by reference.

With reference to the 4 a graphical representation of the lateral force F _lat as a function of the slip angle α for three surface coefficients μ ₁ , μ ₂ and μ _{3 is} shown. In either case, the lateral force generated by a tire increases linearly in the linear range 50 and then reaches a peak value α _p1 . Then the side force in the saturation area decreases 52 , As can be seen, the maximum lateral force F _{latmax corresponds to} a peak value of the slip angle α _p1 in order to generate the maximum lateral force. Therefore, in order to get the best possible control, it is most advantageous to work as close to α _p1 as possible. The present invention provides advantageous conditions in a understeer situation where the grip of the front tires is saturated. Because the vehicle is understeered, the radius of the curve is larger than the driver intended. A reduction in the front wheel slip angle to α _p1 can be achieved by changing the front steering angle by a predetermined amount, which increases the generation of the lateral force of the front tire, which in turn reduces the radius of the curve and thus the understeer rate.

In the case of an oversteering vehicle and one Rear steering, the steering angle of the rear wheels can be changed so that the generation the lateral force of the rear wheels elevated which stabilizes the vehicle.

As from the representation of the 4 can be seen, different surface coefficients μ change the position of the peak values α _p1 , α _p2 and α _p3 .

Another point in the graphical representation of the value μ is a maximum permissible tire slip angle α _mp1 . The maximum allowable angle α _mp1 corresponds to the maximum angle that is desired in the first embodiment of the invention. The maximum permissible angle α _mp1 has a side _slip angle _that is greater than the peak value and therefore has a correspondingly lower side force. In the first embodiment, the side _slip angle is kept at a value between the maximum allowable angle α _mp1 and the peak value angle α _p1 . As will be explained in more detail below, the maximum permissible angle α _{mp1 is} brought closer to the peak value during operation.

wobei
ν_lire = Seitengeschwindigkeit des Reifens u_lire =(u_x) Längsgeschwindigkeit des Reifens entlang der Längsachse (Steuerkurs des Rades (.) α_lire = Schlupfwinkel des Rades

The side slip angle α of the tire can be calculated by various sensors during operation of the vehicle. The slip angle α of the tire is defined as the angle between the controlled course of the wheel and the actual path of the wheel. This is best from the 2 B seen. This means:

in which
ν _lire = lateral speed of the tire u _lire = (u _x ) longitudinal speed of the tire along the longitudinal axis (heading of the wheel (.) α _lire = slip angle of the wheel

Experimentally, v _y and u _x are calculated as follows: to be generally applicable, the equation below has a plus or minus sign, depending on whether the left or right tire is to be calculated.

δ = Lenkwinkel des Rades
u_x = Längsgeschwindigkeit des Fahrzeugs an seinem Schwerpunkt
v_y = Seitengeschwindigkeit des Fahrzeugs an seinem Schwerpunkt
Γ = Gierrate des Fahrzeugs (Rotationsrate um die vertikale Achse)
t = Spurweite des Fahrzeugs (seitlicher Abstand zwischen den Rädern)
a = Längsabstand vom Schwerpunkt des Fahrzeugs zur Achse des Rades (entlang der Achse des Fahrzeugs)
wobei v_x und v_y die Längs- und die Seitengeschwindigkeit des Fahrzeugs an seinem Schwerpunkt sind, gemessen in den in der Karosserie feststehenden x- und y-Richtungen.

δ = steering angle of the wheel
u _x = longitudinal speed of the vehicle at its center of gravity
v _y = lateral speed of the vehicle at its center of gravity
Γ = yaw rate of the vehicle (rotation rate around the vertical axis)
t = track width of the vehicle (lateral distance between the wheels)
a = longitudinal distance from the center of gravity of the vehicle to the axis of the wheel (along the axis of the vehicle)
where v _x and v _{y are} the longitudinal and lateral speeds of the vehicle at its center of gravity, measured in the x and y directions fixed in the body.

A first embodiment of the invention will be described with reference to FIG 5 shown. In this embodiment, the sensors are read in step 60. These sensors can either be all sensors or just some of those in the 3 shown sensors. From these sensors, a coefficient of friction for the surface of the road is determined in step 62. An example of a formula for determining the coefficient of friction of the surface of the road is the following formula:

By determining the coefficient of friction, a maximum permissible tire slip angle α _{mp1 is calculated} in step 64. In step 66, a side slip angle α is determined based on the calculations of the sensors from step 60.

The controller unit 26 changes the position of the steering actuator in direct response to the angle of the hand steering wheel. In the present application, the steering actuator is preferably a steer-by-wire steering system which, in addition to the inputs made via the steering wheel, adds further inputs in order to prevent a predetermined slip angle from being exceeded and thus to maximize the possibilities of control over the vehicle.

A change δ _{Δ of} the steering wheel actuator is calculated in step 68 and is based on the calculated side slip angle and the maximum permissible slip angle calculated in step 64. That is, if the calculated side slip angle is greater than the maximum permissible side slip angle, the position of the steering wheel actuator is changed in step 70 by the amount δ _Δ . Since this is an iteration process, step 60 is repeated again. That is, since the road conditions are constantly changing, the new friction coefficients, the maximum allowable side slip angles and the changes in the steering angle have to be updated continuously so that the maximum allowable side slip angle can approach the peak value α _p . This process continues until the calculated side _slip angle approximately corresponds to the maximum permitted side _slip angle α _mp or the driver commands a reduced steering angle, whereby the calculated side slip angle becomes smaller than the maximum permitted side _slip angle α _mp .

It should be noted that the change δ _{Δ in} the position of the steering actuator is independent of the change in the position of the steering wheel of the vehicle. That is, the changes calculated in steps 60-70 are in addition to the changes made via the steering wheel. Through constant monitoring of the steering angle, the change δ _{Δ in} the position of the actuator for the steering can be extremely extensive in order to compensate for all changes in the steering wheel position that are made by the driver of the vehicle. It should also be noted that this method can be carried out for both front-steering and rear-steering or for independently controlled steering actuators of a vehicle.

With reference to the 6 the method can also monitor the lateral force F _lat and determine a steering change caused thereby. In step 80, the sensors are read in a manner similar to step 60. The various sensors can be all or some of those in the 3 shown sensors include. In step 82, the lateral force acting on the wheels and the side slip angle are calculated on the basis of the sensors read in step 80. The lateral force can be calculated using a filtered lateral acceleration signal a _y . That is, F _lat = ma _y , where m is the (estimated) mass of the vehicle.

In step 84, a change in the angle of the steering actuator is calculated to reduce the slip angle of the tire. In step 86, the recalculated to determine if it has increased. If the lateral force has not increased (N), step 84 is repeated again. If the lateral force has increased (Y), step 88 is carried out in step 86. In step 88, the change in the position of the steering actuator is determined. In step 90, the side force is checked to see if it has decreased. If the lateral force has not decreased (N), step 88 is carried out again. If the lateral force has decreased in step 90 (Y), the process is repeated starting with step 80. This approximation method can be used to optimize other side effects of the vehicle, such as yaw, side slip of the vehicle, β.

As can be seen, this monitors in the 6 shown method continuously the lateral force acting on the wheels. It can be said that the 6 a peak values seeking process is such that the peak value of a _p, corresponding to the maximum side force F _LatMax is obtained. It should also be noted that this second method is not dependent on changes in tire and vehicle parameters, radial loads, wheel camber changes, tire pressure and wear, and changes in slip angle. Due to the constant monitoring of the lateral force, the slip angle is constantly aligned approximately to the value of the tip slip angle α _p .

When performing the two procedures, different ones can be used Types of steering control are carried out by different control signals which depends on the characteristics of the vehicle and the steering system. For example, as described above, a rack and pinion system be controlled to make a desired change to achieve at the rear steering angle by a temporary rear control signal used while the front wheels not changed become. Naturally can change the direction of the front wheels can also be changed by using a front control signal if the back direction changed becomes.

In a system with independently operable front wheels, the relative steering angle between the front wheels can be controlled by the steering 38 be changed without changing or checking the position of the rear wheel. This can be done by independent control of the front wheels or by simultaneous control of the front wheels. Each wheel in an independent system can respond to a corresponding front right, front left, rear right, or rear left control signal.

In a system with independently operable rear wheels, the relative steering angle between the front wheels can be determined by the steering control as a function of the determined rolling behavior 38 be changed without changing or checking the position of the front wheels. This can be done by independent control of the rear wheels or simultaneous control of the rear wheels.

While here are the special embodiments The invention has been shown and described in numerous variations and alternative embodiments for one Expert obviously.

Claims (15)

Control system for a vehicle that has a steering actuator for shows With: a variety of sensors that carry a variety of signals generate that correspond to a dynamic condition of the vehicle, and a controller unit connected to the plurality of sensors, the controller unit being suitable as a function of the measured Vehicle conditions to determine a coefficient of friction of the road surface, dependent on determine a slip angle from the measured vehicle conditions, a first change the angle of the steering actuator to determine the slip angle until the side force increases, one second change the angle of the steering actuator to determine the slip angle as long as increase until the lateral force decreases. System according to claim 1, characterized in that the steering actuator is an actuator for the right front wheel and an actuator for embraces the left front wheel. System according to claim 1 or 2, characterized in that that the steering actuator of the right front wheel and the steering actuator of the left front wheel independently are controllable from each other. System according to one of the preceding claims, characterized characterized in that the controller unit is designed so that it a front right control signal and a front left control signal can generate by making a first change in the angle of the steering actuator and a second change of the angle of the steering actuator is determined. System according to one of the preceding claims, characterized characterized in that the steering actuator is an actuator a rear Steering actuator and a front steering actuator. System according to one of the preceding claims, characterized characterized in that the controller unit has a rear steering control signal determined by making a first change the angle of the steering actuator and a second change in the angle of the steering actuator determined. Method for controlling a vehicle with A steering actuator comprising the steps of: determining a lateral force as a function of measured vehicle conditions; Determining a slip angle as a function of measured vehicle conditions; Determining a first change in the angle of the steering actuator in order to reduce the slip angle until the lateral force increases; Controlling the steering actuator in response to the first change in the angle of the steering actuator; thereafter, determining a second change in the angle of the steering actuator in order to increase the slip angle until the lateral force decreases, and controlling the steering actuator as a function of the second change in the angle of the steering actuator. A method according to claim 7, characterized in that determining a first change to the Angle of the steering actuator in order to reduce the slip angle as long as until the lateral force increases independently from the position of a hand steering wheel. A method according to claim 7 or 8, characterized in that controlling the steering actuator depending on the first change the angle of the steering actuator and controlling the steering actuator dependent on from the second change of Angle of the steering actuator controlling a front steering actuator includes. Method according to one of the preceding claims, characterized characterized in that the steering actuator control is dependent from the first change the angle of the steering actuator and controlling the steering actuator dependent on from the second change the angle of the steering actuator controlling a rear steering actuator includes. Method according to one of the preceding claims, characterized characterized in that the steering actuator control is dependent from the first change the angle of the steering actuator and controlling the steering actuator dependent on from the second change the angle of the steering actuator controlling a front right Steering actuator includes. Method according to one of the preceding claims, characterized characterized in that the steering actuator control is dependent from the first change the angle of the steering actuator and controlling the steering actuator dependent on from the second change the angle of the steering actuator controlling a front left Steering actuator includes. Method according to one of the preceding claims, characterized characterized in that the steering actuator is dependent on the lateral force is controlled to maximize the lateral force. Method according to one of the preceding claims, characterized characterized in that controlling the steering actuator is changing a Slip angle to maximize the lateral force. Method according to one of the preceding claims, characterized characterized in that controlling the steering actuator is changing a Steering angle includes to increase the lateral force until the lateral force decreases again, after which the steering angle is changed as long until the lateral force increases.